High-Density Information Storage by Means of Magnetic Holography on Amorphous TbFe Thin Films

Abstract

High-density information storage by means of magnetic holography is demonstrated by using amorphous TbFe thin films as a magnetic hologram medium. The object beam, which emerges from a two-dimensional information pattern (in most cases 35 mm photographic films), is focused on TbFe film by a lens using the spatial Fourier-transform pattern. A magnetic hologram, that is, a magnetic domain pattern corresponding to the interference pattern of the object beam and the reference beam, is established on the TbFe film by thermo-magnetic writing. A Q-switched ruby laser (of peak light power=0.6MW and light pulse durations30 ns) was used as the writing light source. An illuminated spot, from 0.2 to 1 mm in diameter, was chosen depending on the size of information. Image reconstruction was done by means of either the Faraday effect (transmitted light) or the polar Kerr effect (reflected light) using a first-order diffracted beam. A He-Ne laser (1 mW or 30 mW) was used for the reconstruction light source. It was confirmed that satisfactory images of not only documents but also picture images can be reconstructed by magnetic holography. The storage density estimated from the preliminary experiment is about 4×10³ characters/mm². Some considerations for improving the reconstructed image quality are also described.